A7N8X - Dual DDR Memory Question

[Matt]

I have 2 x 256 2700 sticks and 1 x 512 2700 sticks.

Quick question:

Slots 1 & 3: 256
Slot 2: 512

or

Slot 1: 512
Slots 2 & 3: 256?

I have gone for the former. I'm guessing it will utilise dual ddr better to
have 2 of the same memory in 1 & 3.

Am I right?

Matt

 

[Serial # 19781010]

I have 2 x 256 2700 sticks and 1 x 512 2700 sticks.
Slots 1 & 3: 256
Slot 2: 512

Slot 1: 512
Slots 2 & 3: 256?

I have gone for the former. I'm guessing it will utilise dual ddr better to
have 2 of the same memory in 1 & 3. Am I right?

No. You must have equal amounts of memory in each channel so go for
the latter.

 

[Ron]

My goodness...this issue just seems to cause so much hand-wringing. (And
I'm not being critical, because my hands get wrung too!)

When I built this system, I put a pair of 256's in 1 & 3 too. Then last
week I added a 512 in between. AFAIK it's fine. And by "fine" I mean the
whole 1024 is running in d/c. But then somebody comes along and says no,
and...well...I start wringing again.

I guess I'm still a bit unclear on the whole bank/bus/slot/channel
relationship. Ben has patiently explained it over and over, but for some
reason I find it difficult to comprehend.

Perhaps someone could re-phrase the explanation. (Naturally we'd like to
install the sticks in the best possible config!) Meanwhile, it's comforting
to see that I'm not the only one!

Regards,
Ron

 

[Matt]

My goodness...this issue just seems to cause so much hand-wringing. (And
I'm not being critical, because my hands get wrung too!)

When I built this system, I put a pair of 256's in 1 & 3 too. Then last
week I added a 512 in between. AFAIK it's fine. And by "fine" I mean the
whole 1024 is running in d/c. But then somebody comes along and says no,
and...well...I start wringing again.

I guess I'm still a bit unclear on the whole bank/bus/slot/channel
relationship. Ben has patiently explained it over and over, but for some
reason I find it difficult to comprehend.

Perhaps someone could re-phrase the explanation. (Naturally we'd like to
install the sticks in the best possible config!) Meanwhile, it's comforting
to see that I'm not the only one!

Regards,
Ron

Well I look at it this way. If I only had 2 x 256 I would use slots 1 and 3
(as per the manual and everything else you read about dual ddr). Seeing as I
only have 3 slots it seems logical that the 512 would go in the middle.

Someone please tell me if I'm right or wrong.

 

[Paul]

Well I look at it this way. If I only had 2 x 256 I would use slots 1 and 3
(as per the manual and everything else you read about dual ddr). Seeing as I
only have 3 slots it seems logical that the 512 would go in the middle.

Someone please tell me if I'm right or wrong.

You should be thinking of it in terms of what the memory has to do.
The memory controller alternates between two stacks of memory bytes.
It is like the memory is 128 bits wide, instead of 64, so two stacks
("channels") are used. The processor is only 64 bits wide, so it
gets data from one stack and then the other. Doing this doubles the
rate that the memory can deliver data, as each stack can be working
on the problem at the same time.

With 2 x 256MB, you put one stick on each channel -

------- ------- ^
| 256MB | | 256MB | | equal height in each stack of bytes
------- ------- v

When you add 512MB, you need to rebalance the heights of the stacks.
If you placed the 512MB in the middle slot, I think that would be
256MB in one stack and 768MB in the other stack. That configuration
cannot go back and forth properly, once you get past the initial
matched 256MB on each stack.

Placing the 2 x 256 on one channel, and the 512 on the other,
means "dual channeling" can be used for all the memory.

------- ------- ^
| 256MB | | | |
------- | 512MB | | equal height in each stack of bytes
------- | Stick | |
| 256MB | | | |
------- ------- v

Not that this is that important. On the Nforce2, it seems other
optimizations mean that the dual channel thing doesn't give that
much of an additional performance boost. So the difference between
a misconfigured and a properly configured system is too small to
care about.

HTH,
Paul

 

[Hal]

I tend to agree with Paul, I just went through this yesterday. Had 2x256
and added a 512 in slot 3. Works dual channel fine. 512 also works dual
channel in slot one, but I do not think it will be a balanced system in
slot 2, I need to try this and se if dual channel comes up after post!

The revised owners manual page about memory at the Asus web site implies
that you can install memory in any config and mix but for dual channel
you must install in 1 & 3 or 2 & 3 for 2 sticks and 1,2,3 for 3 sticks.

I have another machine that I am testing 3 sticks of 256 in and the bios
says dual channel and memtest86 is indicating the correct speed. I have
to assume the bios knows and that the upper 256 meg is not running in
single channel mode.

In other words it seems that the amount of memory doesn't matter for
dual channel as long as you install in 1 & 3 or 2 & 3 for 2 sticks and
1,2,3 for 3 sticks. BTW, my 3 stick machine with 3 256 meg modules says
RAM is in ROWS 0,2,4.

I welcome you flames!

Hal

(e-mail address removed) (Paul) wrote in

 

[Matt]

I have 512 in slot 2 and dual channel comes up after post. But then again
there is memory in every slot so I would expect it to do that.

I think I will put my 512 in slot one however after reading Pauls post.

 

[Ben Pope]

I have 2 x 256 2700 sticks and 1 x 512 2700 sticks.

Quick question:

Slots 1 & 3: 256
Slot 2: 512

or

Slot 1: 512
Slots 2 & 3: 256?

I have gone for the former. I'm guessing it will utilise dual ddr
better to have 2 of the same memory in 1 & 3.

Am I right?

Matt

OK guys... here I go!

Neither of those two configurations are what I would call "ideal".

The 512MB DIMM should go in slot 3, as slot 3 comprises the second bank,
each bank is connected to its own channel. The two 256MB DIMMs should go in
slots 1 and 2, 'cos they form the first bank. In this configuration, each
bank has 512MB and is thus "balanced" in terms of memory capacity for each
channel.

So in short:
Dual Channel = Two seperate memory channels.
Memory channel 1 is connected to bank 0, which consists of DIMM slots 1 and
2 (the two closest to the CPU).
Memory channel 2 is connected to bank 1, which consists of DIMM slot 3.

Personally I would "balance" the memory in each channel.

However, the nForce2 *does not require* equal capacities, timings, speeds,
manufacturer, model number or anything else in order to function in Dual
Channel mode... it merely requires some RAM connected to each channel.

I don't know how to make it any simpler...

Ben

 

[dgk]

OK guys... here I go!

Neither of those two configurations are what I would call "ideal".

The 512MB DIMM should go in slot 3, as slot 3 comprises the second bank,
each bank is connected to its own channel. The two 256MB DIMMs should go in
slots 1 and 2, 'cos they form the first bank. In this configuration, each
bank has 512MB and is thus "balanced" in terms of memory capacity for each
channel.

So in short:
Dual Channel = Two seperate memory channels.
Memory channel 1 is connected to bank 0, which consists of DIMM slots 1 and
2 (the two closest to the CPU).
Memory channel 2 is connected to bank 1, which consists of DIMM slot 3.

Personally I would "balance" the memory in each channel.

However, the nForce2 *does not require* equal capacities, timings, speeds,
manufacturer, model number or anything else in order to function in Dual
Channel mode... it merely requires some RAM connected to each channel.

I don't know how to make it any simpler...

Ben

So then, if I'm about to buy memory and unsure about 512 or 1g, then I
buy two 256 and put them in 2 and 3. And if I buy a 512 later, that
goes in 3 and the two 256s move to 1 and 2. That sounds like a plan.
Probably better if the 512 is exactly the same type as the 256s but
apparently not a requirement. Thanks Ben. 512 for now and maybe
another 512 if I ever need it.

 

[Ben Pope]

So then, if I'm about to buy memory and unsure about 512 or 1g, then I
buy two 256 and put them in 2 and 3.

Or 1 and 3.

And if I buy a 512 later, that
goes in 3 and the two 256s move to 1 and 2. That sounds like a plan.

Yep.

Ben